Fuel injection system for internal combustion engines



June 23,1970 BASSOT ET AL 3,516,395

FUEL INJECTION SYSTEM FOR INTERNAL COMBUSTION ENGINES Filed Feb. 8. 1968 m/ua/vroes T/RCQUES BA 5507 LOU/5 MON/5 7 WM (a/A2417 United States Patent 3,516,395 FUEL INJECTION SYSTEM FOR INTERNAL COMBUSTION ENGINES Jacques Bassot, Paris, and Louis Monpetit, lEtang-la- Ville, France, assignors to Societe des Procedes Modernes dInjection Sopromi, Les Mureaux, Yvelines, France Filed Feb. 8, 1968, Ser. No. 704,158 Claims priority, applicafigrzr France, Feb. 22, 1967,

rm. (:1. F02d 5/02 US. Cl. 123-139 4 Claims ABSTRACT OF THE DISCLOSURE It is known to make use of electromagnetic injectors for injecting fuel into internal combustion engines.

However, especially in the case of diesel engines, it proves necessary to inject fairly large quantities of fuel at high pressure and very high velocity, while ensuring in addition that a small overall diameter is maintained within the strict limitations usually imposed by the combustion chamber inlet.

In point of fact, the permissible lift of a valve which is controlled by an electromagnet is limited. In respect of a given injection pressure, the delivery therefore varies as a simple linear function of the bearing diameter of the valve whereas the hydrostatic pressure results in the appearance of a force which varies as the square of the same diameter. In consequence, since the force of attraction of an electromagnet is proportional to the area of opposite surfaces, the overall diameter of an injector of this type varies practically in proportion to its delivery. This being the case, a system of this type cannot in practice be adopted to engines which are not originally designed for such an application.

As is also known, electromagnetic slide-valve injectors can be employed in order to overcome the above-mentioned difficulty. However, such injectors suffer from a double disadvantage in that they call for substantial displacements of the moving portion of the slide-valve, thereby entailing fairly long time lags. In addition, the design of this type of injector calls for the presence of a fairly large volume of liquid between the injector orifice and the control slide-valve, thereby disturbing the injection and the combustion to a marked degree.

Finally, it is known that the metering injection pumps which serve to inject fuel at high pressure in respect of a small angle of rotation of the crankshaft of a Diesel engine are extremely costly and difficult both to construct and to maintain in satisfactory working condition.

The present invention is intended to overcome the disadvantages mentioned in the foregoing and is accordingly directed to an electronically-controlled fuel injection system for internal combustion engines which essentially comprises in combination a constant-pressure fuel pump and one or a number of injection units. Each unit consists of a cylinder of relatively small diameter together with its piston which is connected on the one hand with one or a number of injectors and on the other hand with said pump via a check valve and an electrovalve and fur- ICC ther consists of a cylinder of larger diameter which is located coaxially with and in the line of extension of said small cylinder, said large cylinder being fitted with a piston having one face which is applied against said small piston. A connection is additionally provided by means of a three-way valve between said pump and the chamber which is formed both by the other face of said large piston and the closed extremity of said large cylinder. Said three-way valve is operated in synchronism with the rotation of the engine in order to put the chamber of the large cylinder into communication with the pump or with the fuel supply tank in alternate sequence. Finally, an electronic control unit is provided for the electrovalve and so regulated that said electrovalve is held open during a period which is necessary for introducing the quantity of fuel to be injected into the small cylinder and which can be varied by means of said electronic unit as a function of the operating conditions of the engine. During this period, said large cylinder is in communication with the fuel supply tank whilst each injection takes place at the moment when the three-way valve permits the delivery of fuel under pressure from the pump to the large piston which accordingly thrusts the small piston in the downward direction.

By way of example, and in order that the following description may be more clearly understood, a diagrammatic representation of the system in accordance with the invention is given in the single figure of the accompanying drawings.

Referring to this figure, it is apparent that a pump 2 at relatively low pressure draws the liquid to be injected from the supply tank I. Said pump 2 does not have any metering function. The liquid is delivered on the one hand to an electrovalve 3 of known type and, on the other hand, to a three-way valve 10 at 10a and finally to a pressure-regulating valve 13 which returns the excess flow to the supply tank 1. In some applications, a hydraulic accumulator (which has not been shown in the drawings) can be connected at the point which is common to the pump 2, the electrovalve 3, the three-way valve 10 and the regulator 13. The outlet 10b of the three-way valve 10 is connected to the supply tank 1. The downstream outlet of the electrovalve 3 is connected through a check valve 4 to a cylinder 6 in which a piston 5 is slidably mounted. Said cylinder is provided with a second orifice 14 which is connected with the injector proper.

In addition, a piston 7 which is placed above the piston 5 is slidably mounted within a cylinder 8, the upper chamber of which is connected with the inlet lltlc of the threeway valve 10, and is fitted with a spring 9 of low power which maintains the pistons 7 and 5 in continuous contact with each other.

The chamber 15 which is formed between the cylinders 6 and 8 is connected via a pipe 11 to the fuel supply tank. Said chamber collects any leakage which occurs between the cylinder 8 and the piston 7 and between the cylinder 6 and the piston 5. The orifice of the pipe 11 is so disposed that it is closed off as the large piston 7 reaches the end of its downward travel, thereby providing a hydraulic stop.

The valve 3 is controlled electrically from an electronic unit 12 of known type.

The operation is accordingly as follows in the case of a single-cylinder engine:

The engine operates on the one hand the pump 2 and, on the other hand, either directly in the case of a two-stroke engine or at half-speed in the case of a fourstroke engine, the three-way valve 10 which connects 10a and 10b in alternate sequence to I00 and, finally, an electric device (not shown) which is adapted to trigger the electronic unit 12 at the appropriate moment.

It is assumed that the beginning of the cyclic operation is chosen at the moment when the small piston is in the lowermost position (as shown in the figure) immediately after completion of an injection. The unit 12 initiates the opening of the electrovalve 3 during a period Which is calculated by the electronic unit as a function of the momentary conditions of operation of the engine. During this period, as a result both of the controlled position-setting of the three-way valve through which a connection is accordingly established between a and 10b and of the action of the pressure delivered by the pump 2, the liquid which passes through the electrovalve 3 and the check valve 4 penetrates into the cylinder 6 and causes the pistons 5 and 7 to move upwards. Inasmuch as the injector to which the orifice 14 is connected is assumed to be calibrated at a pressure which is higher than the pressure developed by the pump 2, the flow through said orifice is therefore zero. When the electrovalve 3 closes again under the action of the electronic unit 12, an electrically metered quantity of fuel has therefore been fed into the cylinder 6 beneath the piston 5. Inasmuch as the orifices 10c and 1012 are still in communication, the pressure is equal to the supply tank pressure which is increased very slightly by the reaction due to the spring 9. At the moment when the communication between 10b and 10c is cut off as a result of the actuation of the three-way valve 10 and a communication is established instead between 10c and 10m (a substantial time interval being permitted to elapse between these two operations if necessary), the pressure developed by the pump 2 produces action on the piston 7 and discharges the previously metered liquid through the orifice 14. L1 fact, the pressure of the liquid then increases to a value which is several times that of the pump 2, the ratio being equal to the square of the diameters of the pistons 7 and 5. Consequently, the injection is carried out very rapidly at high pressure. When the piston 7 comes to a stop under the action of the hydraulic (or mechanical) stop referred to above, the injection is completed and the cycle can be repeated.

It will be noted that the time of flow through the electrovalve 3 can be considerably longer than the injection time; in fact, the time allowed for the filling of the cylinder 6 can be much longer than the duration of the injection.

It will be noted in addition that the pistons 5 and 7 are of small overall size and may, for example, be respectively 6 and 12 millimeters in diameter. Said pistons can actually be housed within the nozzle-holder, with the result that the distance between the cylinder 6 and the injector is very small, and any rebound of the injector needle or pintle is virtually impossible.

What we claim is:

1. An electronically controlled fuel injection system for internal combustion engines comprising in combination: a fuel supply tank; a fuel pump; at least one injection unit comprising a cylinder of relatively small diameter and an associated small piston slidably disposed therewithin, said cylinder of relatively small diameter being connected to at least one injector, a cylinder of relatively large diameter disposed coaxially with respect to and above said cylinder of relatively small diameter, said relatively large cylinder having an associated large piston slidably disposed therein so that one of the faces of said large cylinder is capable of being urged against the face of said small piston furthest removed from said injector, a chamber being formed by the other face of said large diameter piston and the closed extremity of said large cylinder; means for controlling the length of stroke of said small and large pistons by providing a precisely measured charge of fuel to said small cylinder, said means comprising: an electrovalve, said electrovalve being connected between said small diameter cylinder and said fuel pump, electronic control means connected to said electrovalve for opening said electrovalve for a period of time determined by engine parameters so as to allow the introduction of a measured charge of fuel from said pump into said small diameter cylinder, a source of pressure, and means connecting said source of pressure directly to said chamber, so that injection of said measured charge of fuel takes place at a time when the pressure exerted by said pressure source is sufficient to displace said large piston and said small piston.

2. A fuel injection system as set forth in claim 1, wherein said pressure source is constituted by said pump; a three-way valve connected between said pump and said chamber; means for controlling said three-way valve in synchronism with the rotation of the engine so that said chamber is alternately put into communication with said pump and with said fuel supply tank; said electronic control unit being regulated so that said chamber is in communication with the fuel supply tank while fuel is being injected into said small cylinder and so that injection takes place at the moment when said three-way valve permits the delivery of fuel under pressure from said pump to said large piston.

3. A fuel injection system as set forth in claim 1, including leakage return means connected between the portion of said large cylinder adjacent said small cylinder and said fuel supply tank.

4. A fuel injection system as set forth in claim 3, wherein the connection of said leakage return means to said large cylinder is so disposed that said large piston seals off the connection at the end of its downward travel so as to form a hydraulic stop.

References Cited UNITED STATES PATENTS 1,803,666 5/ 193 1 French. 2,598,528 5/1952 French 123139.9 2,630,761 3/ 1953 Mashinter 123-1399 LAURENCE M. GOODRIDGE, Primary Examiner U.S. Cl. X.R. 123-32 

